VISITS TO THE MOON AND PLANETS
These are not the actual distances, but they are so close to them that the extra convenience of being able to remember them or to write them down out-weighs the disadvantage of inaccuracy for many purposes.
The law which helps us to remember them was first stated by a man called Titius, and we ought to call it by his name if every one had his rights; but Bode made a sensational use of the law, and so it is generally known as Bode's Law. You can easily see what it amounts to: write down a set of 4's, and add to them other numbers which are doubled every time, beginning with 3 for Venus. The easiest way to remember it is to try and remember that the Earth's distance comes out 10; and perhaps also that Saturn is 100; from these two facts you could recover the law if you had forgotten it.
Let us spend a moment or two on the use made of the law by Bode, about the end of the eighteenth century. At that time there was a break in the series, for none of the minor planets had been found. Nowadays we know nearly 1000 of these little bodies; many of them are very tiny, only a few miles in diameter. They are probably made of the same kind